1. Field of the Invention
The present invention relates to a suspension used in an apparatus for reproducing a sound such as a voice, music or a dial tone, and an electro-acoustic transducer using the same.
2. Description of the Related Art
A conventional electro-acoustic transducer is demonstrated hereinafter with reference to FIGS. 8, 9A and 9B. FIG. 8 is a sectional view of the electro-acoustic transducer. FIG. 9A is a plan view of a diaphragm. FIG. 9B is a sectional view of FIG. 9A taken along the line 9B-9B. In FIG. 8, diaphragm 6 generates aerial vibration. Diaphragm 6 is fixed to frame 11 by frame fixing part 4 through suspension 1 which has vibrating functions and supporting functions. Suspension 1 is of a semicylindrical shape in a cross section and uniform in a circumference direction. Diaphragm 6 is coupled with voice coil 10. Voice coil 10 is placed within magnetic gap 9 of magnetic circuit 8 which is provided at the middle of the frame 11 and formed of plate 13, magnet 14 and yoke 15.
Furthermore, protector 12, for protecting diaphragm 6, is bonded by using an adhesive. An operation of an electromotive loudspeaker structured as disclosed above is described hereinafter.
When a current flows in voice coil 10, the current crosses a magnetic field in magnetic gap 9 at right angles, and a driving force generated at voice coil 10 is transmitted to diaphragm 6. Then suspension 1 supports voice coil 10 in a manner that voice coil 10 becomes concentric with plate 13, and works as a spring in a vibrating direction when diaphragm 6 vibrates. When an alternating current (e.g., a voice signal) flows in voice coil 10, voice coil 10 and diaphragm 6 vibrate while being supported by suspension 1. As a result, air vibrates and a compressional wave is generated, so that a sound can be heard. For example, Japanese Patent Unexamined Publication (H5-103395) is known as a related art of this invention.
However, the conventional suspension has a uniform disk shape in a circumference direction and a closed structure. Therefore, as shown in an arbitrary point P of FIG. 5, which is a sectional view of the suspension in vibration and demonstrated later, when the suspension vibrates by ΔX, a radius of point P changes by Δr, so that force is generated in a circumference direction.
This force is easy to be generated according as the suspension vibrates at large amplitude. As shown in line “A” of FIG. 4, which is a force-displacement characteristic and demonstrated later, compliance becomes non-linear at the large amplitude. Non-linearity of the compliance of supporting force, which is caused by a shape of suspension 1, causes distortion particularly in reproduction of a low tone area where amplitude becomes large.
Compliance of the suspension becomes difficult to maintain due to the phenomena discussed above, so that harmonic distortion is generated at sound pressure frequency characteristics. In addition, a deformation of the suspension is also induced, thereby causing a rolling phenomenon of the diaphragm.